In connection with scales of this type, the price per unit of weight, for example the price per kilogram, of the product to be weighed, which has been placed on the scales, is entered on the input keyboard. By entering the price in this way, the logic device calculates automatically the final price of the product weighed. In particular, if the scales are used as self-service scales, the key fields of the keyboard are normally made in the form of symbol keys, where the individual key fields have symbols (pictographs) which clearly indicate to the self-service customer all individual items of the total range of goods provided for self-service. The self-service customer is then in a position to enter in a particularly simple manner the price per unit of weight of the product to be weighed by actuating a single key field.
In connection with known scales of the type mentioned above such as that disclosed in German Utility Model DE-GM 87 00 968, the capability of changing the writing or symbols assigned to the individual key fields in accordance with the actual range of goods available is known. Such changes in the range of goods occur particularly frequently in connection with fruit stands or with special sales in self-service stores. But, because the number and arrangement of the key fields remains unchanged, the predetermined number and size of the key fields corresponds to a pre-set maximum number of individual goods within a range of goods. Therefore, with respect to a range of goods comprising a small number of individual goods, part of the key fields remain unused. However, it would be desirable to have available, instead of the unused portion of the keyboard, a smaller number of larger key fields corresponding to the smaller range of goods. This would particularly improve the legibility of the input keyboard.